Nosocomial infections (NI) are increasingly recognized causes of morbidity, added hospital costs, and mortality in industrialized countries. Limited available data in developing countries suggest that NI are common and nosocomial diarrhea (ND) appears to be severe and common illness in these countries (1). The objective of this project is to establish and validate an active NI surveillance system at the Hospital Walter Cantidio in the Northeastern Brazil, and thereby determine the epidemiology, possible predisposing risk factors, clinical outcome, added hospital days and costs of ND. The first six months of this project will be used to train the infection control team and set up the NI surveillance system. After this period we shall validate the system with a thrice weekly review of all hospital records and conduct prospective surveillance of all NI and a case-control study of ND over 4 years in this hospital. The last six months of this study will be used to complete the laboratory work and analysis of the data for publication. The NI surveillance will be conducted by three trained nurses each visiting one third of the hospital wards twice a week to consult the nursing care plan book (kept on each ward) to identify high risk patients for NI and patients with ND. Once a high risk patient or a ND case has been selected his medical charts will be reviewed by the nurse to determine the presence of NI or ND, and collect data in a standardized NI form containing information about NI and ND. To study the frequency, potential etiologies and impact of ND in addition to analysis of the surveillance data, fecal specimens from 200 randomized cases of active diarrhea and 200 matched controls without diarrhea will be reviewed and demographic data and risk factors for ND extracted for comparison with diarrhea cases. This project will establish and validate an active infection surveillance program at the Walter Cantidio Hospital and will determine the epidemiology, morbidity, mortality, potential etiologies and impact of ND and its relationship with other NI.